1. Field of the Invention
The present invention relates to an electrical heating element for vertical installation.
2. Description of the Related Art
This type of heating element has a number of resistance elements that run vertically, which resistance elements are supported by a central rod that is fixed attached to a furnace ceiling or similar. A radiative tube is positioned outside of the resistance elements, which radiative rod surrounds the resistance elements.
Such resistance elements are used principally for the heating of furnaces in industrial use. The elements consist of molybdenum silicides or an alloy of molybdenum silicide or Fe—Cr—Al material or Ni—Cr or Ni—Cr—Fe material.
Each element consists of conducting legs that run downwards and upwards a number of times. The resistance element at the top transitions into a number of terminals, which are connected to one or several sources of power. The resistance element thus hangs from the ceiling of the furnace, and extends vertically downwards during operation. The legs are exposed during operation to severe thermal variation, as a result of the development of power in the legs. The consequence of this variation is that the individual legs of the element are bent or twisted when the temperature is changed. A number of ceramic disks, therefore, are placed along the length of the element, provided with holes, through which holes the particular legs of the element pass. The function of these disks is to maintain the separation of the legs of the element such that these do not make contact with each other. Should such a contact arise, the element will be short-circuited, resulting in destruction of the element.
The ceramic disks are held in place by ceramic rods and ceramic tubes.
The uppermost ceramic disk supports, or the uppermost disks support, the weight of the resistance elements. This takes place according to the prior art in that the legs are connected in pairs with the aid of conducting plates, which plates, depending of the actual geometry of the resistance element, rest on the uppermost ceramic disk or disks. Thus the legs run in pairs through a suspension ceramic disk and are connected at the upper surface of the ceramic disk by such a conducting plate and are supported in this way by the ceramic disk.
The uppermost ceramic disk is attached, or the uppermost ceramic disks are attached, to a central rod of a metallic material.
The uppermost ceramic disk supports, or the uppermost ceramic disks support also the weight of the ceramic items that are present.
It is required to produce long such elements. It is a wish that the heating element should have a length that exceeds 2,500 mm. At such a length, the length is such that the thermal expansion of the resistance elements can no longer be managed.
This is a result of the fact that at high temperatures and when using long elements, the mechanical load on the metallic central rod, which supports the weight of the resistance elements and the said ceramic items that ensure the relative positions of the resistance elements, becomes so great that the rod becomes deformed.
Thus, the basic problem is that the weight of the resistance elements and the necessary ceramic items becomes too great.
The present invention solves this problem and allows the design of resistance elements with a length that exceeds 2,500 mm.
The present invention thus relates to an electrical heating element for vertical installation, comprising vertically suspended electrical resistance elements for the heating of furnaces in industrial operation, where each element consists of conductive legs that run downwards and upwards a number of times, where along the length of the element there are placed a number of ceramic disks provided with holes, through which holes the relevant legs of the element pass, and where the element at its upper end transitions into terminals that are connected to a source of power, where the said ceramic disks are arranged between ceramic tubes and where an upper metallic central rod is positioned within the ceramic tubes, which central rod is fixed to the ceiling of the furnace and which supports the element through at least one of the uppermost of the said ceramic disks and where the element is surrounded by a radiative tube, and it is characterised in that there are a number of upper ceramic tubes outside of the upper central rod, with intermediate ceramic disks, in that the ceramic disks are positioned at a distance from each other and outside of the central rod, in that the central rod extends a certain distance down into the radiative tube, in that a number of lower ceramic tubes with intermediate ceramic disks are positioned outside of a lower central rod, in that the ceramic disks are positioned at a distance from each other and outside of the lower central rod, in that the lower central rod extends a certain distance up from the bottom of the radiative tube to a level somewhat lower than the lower end of the upper central rod, and in that the lower central rod and the lowermost of the lower ceramic tubes are supported by the bottom of the radiative tube, whereby the weight of the to lower central rod and its associated ceramic items is supported by the radiative tube.
The invention will be described in more detail below, partially in association with the attached drawings, where
Outside of the upper central rod there are, according to the invention, a number of upper ceramic tubes 15, 16, 17 with intermediate ceramic disks 3. The ceramic disks 3 are located at a distance from each other and outside of the central rod 11. The central rod 11 extends a certain distance down into the radiative tube 14. Furthermore, there are a number of lower ceramic tubes 18, 19, 20 with intermediate ceramic disks 3 outside of a lower central rod 21. The dashed lines 22, 23 in
According to one preferred embodiment, see
It is preferred that the said zone 28 comprises a ceramic sheath 29 that surrounds the lower part 30 of the upper central rod 11 and the upper part 31 of the lower central rod 21, where the end surfaces 26, 27 of the central rods are located at a distance from each other independent of the current temperature. The ceramic sheath 29 is supported by the uppermost ceramic disk 33 of the lower ceramic disks 33, 3, 23.
According to a first embodiment shown in
The lowermost ceramic disk 38 of the upper ceramic disks is supported in
According to a further preferred embodiment, the element 2 can be displaced relative to all ceramic disks except for the uppermost ceramic disk or disks 12, 13 and the ceramic disk 34 that is located in the said zone 28.
According to a second embodiment shown in
In the case of the second of the said embodiments, it is preferred that the element 2 can be displaced relative to all ceramic disks except for the uppermost disk or disks 12, 13.
There is thus achieved through the present invention a reduction of load with respect to the mechanical load on the metallic central rod that supports the weight of the resistance elements and the said ceramic items that ensure the relative positions of the resistance elements, whereby deformation of the upper central rod is avoided.
A number of embodiments have been described above. It is however obvious that heating elements of the specified type can be constructed for instance with more or fewer ceramic disks with intermediate ceramic tubes.
The present invention is therefore not to be regarded as being limited to the embodiments specified above, since it can be varied within the scope of the attached patent claims.
Number | Date | Country | Kind |
---|---|---|---|
0501314 | Jun 2005 | SE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/SE2006/060157 | 5/24/2006 | WO | 00 | 12/7/2007 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2006/132590 | 12/14/2006 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
1618364 | Clark et al. | Feb 1927 | A |
2790889 | Hynes | Apr 1957 | A |
3571566 | Kuzara | Mar 1971 | A |
4011395 | Beck | Mar 1977 | A |
4016403 | Best | Apr 1977 | A |
4179603 | Zeigler et al. | Dec 1979 | A |
4272639 | Beck | Jun 1981 | A |
RE30838 | Best | Dec 1981 | E |
4322606 | Bayly | Mar 1982 | A |
4771166 | McGuire et al. | Sep 1988 | A |
4813805 | Dagata | Mar 1989 | A |
5338918 | Eshleman | Aug 1994 | A |
5473141 | Makris et al. | Dec 1995 | A |
5497394 | Jhawar et al. | Mar 1996 | A |
5543603 | Schmadig et al. | Aug 1996 | A |
7439473 | Lewin | Oct 2008 | B2 |
7576306 | Lewin | Aug 2009 | B2 |
7692122 | Lewin et al. | Apr 2010 | B2 |
Number | Date | Country |
---|---|---|
2005006812 | Jan 2005 | WO |
Entry |
---|
International Search Report included in Published PCT Application Serial No. PCT/SE2006/050157 Published Dec. 14, 2006. |
Number | Date | Country | |
---|---|---|---|
20100193504 A1 | Aug 2010 | US |